There is a demand to form an image by using an in-line printer that prints an image, such as a manufacturing date, on an image forming target object, such as packaging material formed of a transparent material, such as polyethylene or the like, via an electrophotographic method. The electrophotographic method is an image forming method in which an image is formed by toner by charging a photoconductor. An in-line printer that forms an image via the electrophotographic method needs to transfer toner to the image forming target object that has been conveyed, and then fix the toner on the image forming target object. Such an in-line printer may fix the toner by irradiating light, such as visible light, infrared rays, or the like. However, when the toner is fixed by being irradiated with the light, a flash process of irradiating the light needs to be performed after a transfer process of transferring the toner is performed. In such an in-line printer, a transfer unit that performs the transfer process and the flash unit that performs the flash process are sequentially arranged in a direction of conveyance of the image forming target object. In this regard, the in-line printer that forms an image via the electrophotographic method becomes large-scaled.